The field of this invention is heat exchangers, and, more particularly, ultra low mass radiators intended for aerospace power and thermal management applications using a single phase working fluid pumped loop.
The waste heat generated by power systems, instrumentation, and life support in spacecraft must be radiated into space using lightweight radiators. The primary system optimization criterion for most spacecraft systems is to minimize the specific mass, with efficiency and cost being of secondary importance. The most massive single component in space power systems such as Stirling cycles and closed Brayton cycles is the radiator. Current large radiator systems have a total mass of about 10 kg/m.sup.2, although some proposed designs hope to achieve half that amount. The radiator often accounts for the majority of the total system mass in large power systems.
Systems utilizing heat pipes and biphasic fluids such as the carbon-fiber-augmented design by Olsen, U.S. Pat. No. 4,603,731, have been found to be suitable for low power systems. The honeycomb sandwich heat pipe design by Tanzer, U.S. Pat. No. 4,830,097 may have some advantages in small, high temperature systems. The pumped loop expandable coil design by Mahefkey, U.S. Pat. No. 4,727,932 appears inexpensive, but it is extremely vulnerable. The gas-particle concept by Chubb, U.S. Pat. No. 4,770,232, and the liquid droplet concept by Webb, U.S. Pat. No. 4,789,517 are also extremely vulnerable and susceptible to single-point failure. All of the above systems suffer from high specific mass (5-20 kg/m.sup.2). Most of the prior art also suffers from a narrow range of effective radiating temperatures--typically 400-600 K., although some, such as that by Mims, Buden, and Williams, U.S. Pat. No. 4,832,113, are intended for 1000-1300 K.
The instant invention is a radical departure from the prior art in that all attempts to augment total surface area relative to tube surface area (e.g, the use of fibers or fins) are expressly avoided. A poor thermal conductor such as titanium--will often be used. The design problem is primarily a mechanical problem rather than primarily a thermal problem. The goal is to minimize radiating surface mean thickness while satisfying stiffness and protection requirements. This is achieved through the use of tubular radiating structures of small diameter in a modular design that permits numerous strengthening cross members and protective coatings. The modules are in some respects similar to the MTS exchangers by Doty and Spitzmesser of U.S. Pat. Nos. 4,676,305, 4,896,410, and 4,928,755.
Ceramic fiber shields, similar to those of Collings and Bannon, U.S. Pat. No. 4,850,337, are used for protection against space debris. Deakin, U.S. Pat. No. 4,911,353, discloses a metal spray technique for producing selective coatings.